Aqueous hydrolysis of pyrazol-1-ylacetates

K. S. Badalyan 0 A. G. Asratyan 0 O. S. Attaryan 0 0 Institute of Organic Chemistry, National Academy of Sciences of Armenia , pr. Azatutyan, 26, Yerevan, 00014 Armenia - The pyrazole esters (n = 2) are known to be hydrolyzed in the presence of bases [13]. We found that pyrazole esters IIII (n = 1) are hydrolyzed with water in the absence of bases. R1 R1 IIII CH2C IVVI CH2C OH I, IV, R1 = R2 = H; II, V, R1 = CH3, R2 = H and R1 = H, R2 = CH3; III, VI, R1 = R2 = CH3. This behavior of the esters IIII is apparently caused by the negative inductive effect of pyrazole ring. This is supported by the fact that the reaction time increases 2.5 times when passing from compound I to compound III. Another important fact which must be taken into account when considering the mutual influence of the directly bonded atoms is the proximity of the pyrazole ring to the carbonyl carbon. As the distance between the atoms increases (n = 2), the electrophilicity of the carbonyl carbon decreases, therefore the stability of esters with respect to water increases. Pyrazol-1-ylacetic acid (IV). A mixture of 5 g of compound I and 25 ml of water was heated at 100C for 10 h. After cooling, the mixture was alkalinized with an aqueous solution of Na2CO3 and extracted with 50 ml of ether. The aqueous solution was evaporated to a half volume and neutralized with hydrochloric acid. The resulting crystals were filtered off. Yield 2.5 g (70%), white crystals, mp 175178C (water). IR spectrum, , cm1: 1530 (ring), 1700 (C=O), 31003400 (COOH). 1 NMR spectrum (DMSO-d6), , ppm (J, Hz): 4.84 s (2H, CH2), 6.19 d.d (1H, 4-, J 2.3, 1.8), 7.34 d (1H, 5-H, J 1.8), 7.57 d (1, 3-, J 2.3), 12.63 br.s (1, ). Found, %: 47.85; 4.38; N 22.51. 56N22. Calculated, %: 47.61; 4.76; N 22.22. 3(5)-Methylpyrazol-1-ylacetic acid (V) was obtained similarly from 5 g of the ester II, the reaction time was 3,5-Dimethylpyrazol-1-ylacetic acid (VI) was prepared similarly from 5 g of the ester III, the reaction time is 25 h. Yield 2.7 g (65%). White crystals, mp 188 190C (water) [5]. IR spectrum, , cm1: 1540 (ring), 1700 (C=O), 33003400 (). 1 NMR spectrum (DMSO-d6), , ppm (J, Hz): 2.11 s (3H, 3-CH3), 2.18 s (3H, 5-CH3), 4.63 s (2H, NCH2), 5.71 s (1, 4-), 12.57 br.s (1, ). Found, %: 54.85; 6.73; N 18.32. 710N22. Calculated, %: 54.54; 6.49; Br 45.71; N 18.18. The IR spectra were registered on a Specord IR-75 instrument from KBr pellets. The 1 NMR spectra were recorded on a Varian Mercury-300 spectrometer in DMSO-d6. The initial pyrazol-1-ylacetates IIII were obtained by the known methods [4]; ethyl pyrazol-1-ylacetate (I): bp 9598C (3 mm Hg), nD20 1.4690; ethyl 3(5)-methylpyrazol-1-ylacetate (II): bp 104108C (3 mm Hg), nD20 1.4620 [the isomers ratio is (3:5)(4:1)]; ethyl 3,5-dimethylpyrazol-1-ylacetate (III): bp 110115C (3 mm Hg), n2D0 1.4700. (...truncated)